In the conventional configuration of the antenna device, the antenna field pattern of different frequency bands will point in different directions. For example, the low frequency antenna pointing forwards and the high frequency antenna pointing backwards; or the low frequency antenna transmits to the side and the high frequency antenna transmits to the front. If it is expected that the antenna field patterns of different frequency bands point in the same direction, the configuration of the conventional antenna device will require a larger antenna volume so that the antenna field patterns of different frequency bands point in the same direction.
Therefore, how to design a directional antenna with multiple frequency bands (at least two frequency bands) in a small space size and control the main beam of the antenna field pattern in different frequency bands to point in the same direction is one of the problems to be improved in the field.